Triangular printing stamp



FIG. 1 is a bottom perspective view of a triangular printing stamp showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a right side elevation view thereof, the left side elevation view being a mirror image; and,

FIG. 5 is a rear elevation view thereof.

The broken lines showing portions of the printing stamp form no part of the claimed design. 

The ornamental design for a triangular printing stamp, as shown and described. 